The relationship between the increased synthesis of proteases and the transformed cell phenotype will be examined in two ways. First we will test the contribution of proteases to the transformed phenotype by examining the effect of protease inhibitors in several in vitro and in vivo assays for transformation. Protease inhibitors with specificities for collagenase, plasminogen activator, thiol proteases, and plasmin will be purified from specific tissues. These will include cartilage (collagenase and thiol protease inhibitors), which is known to be resistant to tumor invasion, and placenta, which is rich in a plasminogen activator inhibitor. The purified protease inhibitors will be tested for their effects on transformation-associated parameters such as growth in Methocel, wound migration, invasion, and neovascularization. Any experimentally induced modifications in cell phenotype will be correlated with decreases in specific proteolytic activities. Second, sets of cell lines transformed with mutants of SV40 or polyoma virus, unable to code for functional large, middle or little T proteins, will be assayed for the production of the protease plasminogen activator. We will attempt to establish whether the increased synthesis of this enzyme, observed in many transformed cells, can be correlated with the presence of a specific functional viral gene in cells transformed by SV40 or polyoma virus.